1. Field of the Invention
The present invention relates to electronic flash cameras, in general, and to apparatus for avoiding the closure of an intended subject's eyelids during an exposure interval in response to visible light produced by the electronic flash in such a camera if the electronic flash is fired immediately prior to the exposure interval for range related purposes, in particular.
2. Description of the Prior Art
Photographic cameras having means for illuminating a subject to be photographed with infrared and/or visible light for range and/or reflectivity related purposes immediately prior to an exposure interval, have been disclosed in the prior art. In, for example, U.S. Pat. No. 4,357,083 to Johnson et al. a method and apparatus are described in which a subject to be photographed is illuminated with visible and non-visible radiation immediately prior to or at the early stages of an exposure interval. A signal representative of the non-visible radiation reflected from a subject to be photographed is employed, in part, for lens focusing purposes. While this arrangement is effective in determining subject distance, for example, the visible radiation illuminating the scene at these points in an exposure cycle often induces unwanted eyelid closures while a subject is being photographed.
This eyelid closure problem could be avoided by employing non-visible or infrared light at these points in an exposure cycle for subject distance determining purposes. In U.S. Pat. No. 3,173,347 to Stimson et al., a subject to be photographed is illuminated by two sources of artificial illumination at different times during an exposure cycle. One source illuminates a subject to be photographed with infrared light immediately prior to an exposure interval in order to derive a signal representative of subject distance and/or reflectivity for the purpose of automatically establishing an exposure aperture in response to this infrared light derived signal. The other source of light illuminates the subject to be photographed with visible light for photographic recording during the exposure interval. This arrangement avoids the problem of inducing eyelid closure mentioned above with respect to the Johnson et al. patent. However, the additional light source significantly increases the size and cost of photographic apparatus employing such an arrangement.
In U.S. Pat. No. 4,229,464 to Cushman, a method and apparatus are described for reducing the incidence of eye closures during the photographing of a human subject. A camera is used in combination with a visible light producing electronic flash and a delay mechanism for controlling the time when the camera shutter will open. The electronic flash is actuated to produce a pre-exposure flash of visible light in order to induce the eyes of the subject to blink. A delay period is also initiated in the camera's controls to delay opening of the camera's shutter. The duration of this delay is such that an exposure is not likely to be made until the refractory period after the evoked involuntary blink has been completed. The refractory period is that period of time after an eye has been stimulated with a first flash of visible light during which the eye is unable to react to a second flash of visible light. At the end of this delay period the shutter is allowed to open and a second flash may be generated to provide supplementary illumination. By delaying exposure until the refractory period immediately after a pre-exposure flash induced eyelid blink, the closure of an intended subject's eyelids during exposure from supplementary illumination is thereby reduced. While this arrangement is effective in reducing the incidence of eyelid closures during exposure, the delay in opening the shutter to produce an exposure interval may interfere with the camera's ability to photograph scenes that are only available during all or a portion of the delay period.